File and Stream Handler Installation

The AVIFile library uses installed stream and file handlers for reading and
writing AVI files and streams. A handler is installed when it resides in the
Windows SYSTEM directory and the registry contains the following information needed
to describe and identify a handler:

The AVIFile library queries the registry for handlers that are external to an
application when opening files and accessing streams. The result of a
successful query returns the filename of a handler that can process the file or stream
type specified in the query. The registry lists each handler by creating three
entries that have the following form:

[HKEY_CLASSES_ROOT\Clsid\{00010023-0000-0000-C000-000000000046}]

@="Wave File reader/writer"

[HKEY_CLASSES_ROOT\Clsid\{00010023-0000-0000-C000-

000000000046}\InprocServer32]

@="wavefile.dll"

"ThreadingModel"="Apartment"

[HKEY_CLASSES_ROOT\Clsid\{00010023-0000-0000-C000-

000000000046}\AVIFile]

@="3"

These entries consist of the following parts.

Part

Description

HKEY_CLASSES_ROOT

Identifies the root entry of the registry.

Clsid

Identifies this entry as a class identifier.

{00010023-0000-0000-C000-000000000046}

Specifies an interface identifier (IID) or class identifier. This value is a
unique 16-byte identifier. (The identifier might also be referred to as a GUID
or a UUID in other manuals.)

Wave File reader/writer

Specifies a string to describe the handler. This string can be displayed in
dialog boxes for selecting stream and file handlers.

InProcServer32

Specifies the file (in this example, WAVEFILE.DLL) that can be loaded to
handle this class.

AVIFile

Specifies the properties of a file handler. In this example, the handler can
read and write to an AVI file.

A file handler can have one or more of its properties stored in the registry.
The following constants identify the properties currently associated with a
file.

Constant

Description

AVIFILEHANDLER_CANACCEPTNONRGB

Indicates that a file handler can process image data other than RGB.

AVIFILEHANDLER_CANREAD

Indicates that a file handler can open a file with read access.

AVIFILEHANDLER_CANWRITE

Indicates that a file handler can open a file with write access.

When creating a file or stream handler, you can obtain a new identifier by
running UUIDGEN.EXE. Always use UUIDGEN.EXE to create a new identifier. The
16-byte hexadecimal number created by this executable will uniquely identify your
handler.

The AVIFile library uses additional entries in the registry to identify a
class identifier based on the file extension that a file handler can process or a
four-character code that a file or stream handler can process. For example, the
following entries associate a class identifier with the file extension .WAV and
the four-character code "WAVE":

[HKEY_CLASSES_ROOT\AVIFile\Extensions\WAV]

@="{00010023-0000-0000-C000-000000000046}"

[HKEY_CLASSES_ROOT\AVIFile\RIFFHandlers\WAVE]

@="{00010023-0000-0000-C000-000000000046}"

These entries consist of the following parts.

Part

Description

HKEY_CLASSES_ROOT

Identifies the root entry of the registry.

AVIFile

Identifies this entry as an entry used by AVIFile.

Extensions

Specifies the file extension (in this example, .WAV) that a file handler can
process.

RIFFHandlers

Specifies the four-character code (in this example, "WAVE") a file or stream
handler can process.

{00010023-0000-0000-C000-000000000046}

Specifies an interface identifier (IID) or class identifier.

If you distribute your stream or file handler without a setup application to
install it in the user's system, you must include a .REG file so the user can
install the handler. The user will use the registry editor to create registry
entries for your stream or file handler.

The following example shows the contents of a typical .REG file. The first
entry in the following example is the descriptive string for the handler. The
second entry identifies the file containing the handler. The third entry identifies
the properties of the file handler (in this case, read-only access to files).
The fourth entry associates the type of file the handler processes (in this
case, files with a .JPG filename extension) with the class identifier.